1. Field of the Invention
The present invention relates to an optical measurement method and an optical measurement apparatus for performing measurement of light which has been emitted from a specimen in response to illumination of the specimen, or has been reflected by or has penetrated through a specimen when the specimen is illuminated, under a condition that background light behaves as background noise. The background light is caused, for example, by room illumination.
2. Description of the Related Art
An optical measurement apparatus performing measurement of light as described above is conventionally known. In such an apparatus, it is not possible to perform precise measurement when light to be measured is incident on an optical detector together with room illumination light and other light from outside as background noise. Therefore, in a conventional technique, the background light is eliminated by an attenuation filter or a spatial filter before the background light is incident on the optical detector, where the attenuation filter attenuates light intensity in a specific wavelength range, and the spatial filter utilizes a pinhole.
Nevertheless, when using the above attenuation filter or spatial filter, it is not possible to separate the light to be measured from the background light when the wavelength range of the background light overlaps the wavelength range of the light to be measured. That is, a portion of the background light is mixed into the light to be measured and the quality of measurement deteriorates.
Alternatively, a technique of shortening an exposure time is proposed. In the technique, the exposure time is made so short, for example, not longer than 100 nsec, that the background light does not affect measurement data. In order to shorten the exposure time to not longer than 100 nsec, a short-pulse light source and a high-speed, high-sensitivity detector (e.g., an image intensifier) are necessary. However, these components are expensive, and therefore increase the manufacturing cost of the measurement apparatus. From the viewpoint of cost reduction, it is not possible to use such expensive components. On the other hand, the exposure time cannot be shortened to less then one micrometer when an inexpensive laser diode and charge-coupled device (CCD) are used. That is, the influence of the background light cannot be eliminated by use of the inexpensive laser diode and charge-coupled device (CCD). Further, even if the laser diode is driven to emit a short-pulse beam and the image intensifier is used for detection, it is not possible to obtain a high peak with a usual operation of driving the laser diode. That is, sufficient exposure energy cannot be supplied to a specimen with the above construction.
The first object of the present invention is to provide an optical measurement method and an optical measurement apparatus which can perform measurement of light with high accuracy even when the wavelength range of the background light overlaps the wavelength range of the light to be measured, which has been emitted from a specimen, or has been reflected by or has penetrated through a specimen when the specimen is illuminated.
The second object of the present invention is to provide an optical measurement method and an optical measurement apparatus enabling precise measurement of light which has been emitted from a specimen, or has been reflected by or has penetrated through a specimen when the specimen is illuminated, under a plurality of types of background light respectively having a plurality of different periods of cyclic intensity variations.
In order to accomplish the above-mentioned first object, according to the first aspect of the present invention, there is provided an optical measurement method for performing measurement of first light, which has been emitted from or reflected by a specimen, or has penetrated through the specimen, under background light having an intensity which varies cyclically with a period. The method contains steps of: (a) performing a first operation of measuring the first light for a first duration beginning at a first time, while illuminating the specimen with second light, to obtain a first measurement result; (b) performing a second operation of measuring the first light for a second duration having the same length as the first duration and beginning at a second time which is different from the first time by an integer multiple of the above period, while illumination of the specimen is stopped, to obtain a second measurement result; and (c) subtracting the second measurement result from the first measurement result, to obtain a third measurement result which is not affected by the background light.
In order to accomplish the above-mentioned first object, according to the second aspect of the present invention, there is provided an optical measurement apparatus for performing measurement of first light, which has been emitted from or reflected by a specimen, or has penetrated through the specimen, under background light having intensity which varies cyclically with a period. The apparatus contains a first measurement unit which performs a first operation of measuring the first light while illuminating the specimen by second light, to obtain a first measurement result; a second measurement unit which performs a second operation of measuring the first light while illumination of the specimen is stopped, to obtain a second measurement result; a control unit which controls timing of the operations of the first and second measurement units so that the first operation is performed for a first duration beginning at a first time, and the second operation is performed for a second duration having the same length as the first duration and beginning at a second time which is different from the first time by an integer multiple of the above period; and a calculation unit which obtains a third measurement result, which is not affected by the background light, by subtracting the second measurement result from the first measurement result.
According to the first and second aspects of the present invention, the difference between the beginning times of the first and second operations of measuring the first light is an integer multiple of the period of the cyclic variation of the intensity of the background light, and the first and second operations are performed for the same length of time. Since the specimen is not illuminated with the second light during the second operation, it is considered that an amount of influence by the background light included in the first measurement result of the first operation will be the same as the amount of the second measurement result of the second operation. Therefore, it is expected that the amount of influence by the background light included in the first measurement result of the first operation will be removed by subtracting the amount of the second measurement result of the second operation from the amount of the first result of the first operation. Thus, a final (third) measurement result can be obtained with high accuracy even when the wavelength range of the background light overlaps the wavelength range of the light to be measured, which has been emitted from a specimen in response to illumination of the specimen, or has been reflected by or has penetrated through a specimen when the specimen is illuminated.
In order to accomplish the above-mentioned first object, according to the third aspect of the present invention, there is provided an optical measurement method for performing measurement of first light, which has been emitted from or reflected by a specimen, or has penetrated through the specimen, under background light having an intensity which varies cyclically with a period. The method contains steps of: (a) performing a first operation of measuring the first light for a first duration having a length equal to an integer multiple of the above period, while illuminating the specimen by second light, to obtain a first measurement result; (b) performing a second operation of measuring the first light for a second duration having a length equal to the length of the first duration, while illumination of the specimen is stopped, to obtain a second measurement result; and (c) subtracting the second measurement result from the first measurement result, to obtain a third measurement result which is not affected by the background light.
In order to accomplish the above-mentioned first object, according to the fourth aspect of the present invention, there is provided an optical measurement apparatus for performing measurement of first light, which has been emitted from or reflected by a specimen, or has penetrated through the specimen, under background light having an intensity which varies cyclically with a period. The apparatus contains a first measurement unit which performs a first operation of measuring the first light while illuminating the specimen with second light to obtain a first measurement result; a second measurement unit which performs a second operation of measuring the first light while illumination of the specimen is stopped, to obtain a second measurement result; and a control unit which controls timing of the operations of the first and second measurement units so that each of the first and second operations is performed for a duration having an identical length equal to an integer multiple of the above period; and a calculation unit which obtains a third measurement result, which is not affected by the background light, by subtracting the second measurement result from the first measurement result.
According to the third and fourth aspects of the present invention, the first and second operations are also performed for the same length of time, and the length is equal to an integer multiple of the above period of the cyclic variation of the intensity of the background light. It is expected that an amount of influence by the background light on a measuring operation for an identical length of time will not change regardless of the beginning time of the measuring operation, when the length of time is equal to an integer multiple of the above period of the cyclic variation of the intensity of the background light. Since the specimen is not illuminated by the second light during the second operation, regardless of the beginning times of the first and second operations, it is expected that an amount of influence by the background light included in the first measurement result of the first operation will be the same as the amount of the second measurement result of the second operation. Therefore, it is expected that the amount of influence by the background light included in the first measurement result of the first operation will be removed by subtracting the amount of the second measurement result of the second operation from the amount of the first measurement result of the first operation. Thus, a final measurement result can be obtained with high accuracy even when the wavelength range of the background light overlaps the wavelength range of the light to be measured, which has been emitted from a specimen in response to illumination of the specimen, or has been reflected by or has penetrated through a specimen when the specimen is illuminated.
In the above first to fourth aspects of the present invention, the period may be obtained by measuring the intensity of the background light. When the period obtained based on the measured intensity of the background light is used for controlling the timing of the measurement operations in the present invention, an accurate value of the period can be used, and therefore the measurement can be performed with higher accuracy.
In addition, in the above first to fourth aspects of the present invention, each of the first and second operations may or may not be performed in synchronization with the cyclic variation of the background light.
Further, the above-mentioned xe2x80x9cfirst light which has been emitted from a specimenxe2x80x9d may be reradiation light such as fluorescent light, Raman scattering light, phosphorescent light, or the like.
The above-mentioned xe2x80x9cfirst light, which has been xe2x80x9creflected by a specimenxe2x80x9d may be light which has been polarized due to the reflection, or has a spectrum not containing a portion of components which has been absorbed by the specimen, or has intensity reduced due to the reflection in accordance with reflectance of the specimen, or has been changed by any combination of polarization, absorption of a spectrum component, and intensity reduction.
The above-mentioned xe2x80x9cfirst light, which has penetrated through the specimenxe2x80x9d may be light which has been polarized during the penetration, or has a spectrum not containing a portion of components which is absorbed by the specimen during the penetration, or has intensity reduced during the penetration in accordance with transmittance of the specimen, or has been changed by any combination of polarization, absorption of a spectrum component, and intensity reduction.
The above-mentioned xe2x80x9cmeasurement of lightxe2x80x9d may include spectrum measurement of light and quantitative or qualitative measurement of intensity of light, and the measurement may be performed at one measurement point or at a number of measurement points. For example, the measurement may be performed by obtaining information on an image containing the measurement points, where such an image may be obtained by using a charge-coupled device (CCD).
In order to accomplish the above-mentioned second object, according to the fifth aspect of the present invention, there is provided an optical measurement method for performing measurement of first light, which has been emitted from or reflected by a specimen, or has penetrated through the specimen, under a plurality of types of background light respectively having a plurality of different periods with which intensities of the plurality of types of background light vary cyclically. The method contains steps of: (a) performing a first operation of measuring the first light for a first duration having a length equal to an integer multiple of the least common multiple of the plurality of different periods, while illuminating the specimen with second light, to obtain a first measurement result; (b) performing a second operation of measuring the first light for a second duration having a length equal to the length of the first duration, while illumination of the specimen is stopped, to obtain a second measurement result; and (c) subtracting the second measurement result from the first measurement result, to obtain a third measurement result which is not affected by the plurality of types of background light.
In order to accomplish the above-mentioned second object, according to the sixth aspect of the present invention, there is provided an optical measurement apparatus for performing measurement of first light, which has been emitted from or reflected by a specimen, or has penetrated through the specimen, under a plurality of types of background light respectively having a plurality of different periods with which intensities of the plurality of types of background light vary cyclically. The apparatus contains a first measurement unit which performs a first operation of measuring the first light while illuminating the specimen with second light, to obtain a first measurement result; a second measurement unit which performs a second operation of measuring the first light while illumination of the specimen is stopped, to obtain a second measurement result; a control unit which controls timing of the operations of the first and second measurement units so that each of the first and second operations is performed for a duration having an identical length equal to an integer multiple of the least common multiple of the plurality of different periods; and a calculation unit which obtains a third measurement result, which is not affected by the plurality of types of background light, by subtracting the second measurement result from the first measurement result.
According to the fifth and sixth aspects of the present invention, the first and second operations are performed for the same length of time, and the length is equal to an integer multiple of the least common multiple of the plurality of different periods of the cyclic variations of the intensities of the plurality of types of background light. It is expected that an amount of influence of the plurality of types of background light on a measuring operation for an identical length of time will not change regardless of the beginning time of the measuring operation, when the length of time is equal to an integer multiple of the least common multiple of the plurality of different periods of the cyclic variations of the intensities of the plurality of types of background light. Since the specimen is not illuminated with the second light during the second operation, regardless of the beginning times of the first and second operations, it is expected that an amount of influence of the plurality of types of background light included in the first measurement result of the first operation will be the same as the amount of the second measurement result of the second operation. Therefore, it is expected that the influence of the plurality of types of background light included in the first measurement result of the first operation will be removed by subtracting the amount of the second measurement result of the second operation from the amount of the first measurement result of the first operation. Thus, a final measurement result can be obtained with high accuracy even when the wavelength ranges of the plurality of types of background light overlap the wavelength range of the light to be measured, which has been emitted from a specimen in response to illumination of the specimen, or has been reflected by or has penetrated through a specimen when the specimen is illuminated.
In order to accomplish the above-mentioned second object, according to the seventh aspect of the present invention, there is provided an optical measurement method for performing measurement of first light, which has been emitted from or reflected by a specimen, or has penetrated through the specimen, under a plurality of types of background light respectively having a plurality of different periods with which intensities of the plurality of types of background light vary cyclically. The method contains steps of: (a) performing a first operation of measuring the first light for a first duration beginning at a first time, while illuminating the specimen with second light, to obtain a first measurement result; (b) performing a second operation of measuring the first light for a second duration having the same length as the first duration and beginning at a second time which is different from the first time by an integer multiple of the least common multiple of the plurality of different periods, while illumination of the specimen is stopped, to obtain a second measurement result; and (c) subtracting the second measurement result from the first measurement result, to obtain a third measurement result which is not affected by the plurality of types of background light.
In order to accomplish the above-mentioned second object, according to the eighth aspect of the present invention, there is provided an optical measurement apparatus for performing measurement of first light, which has been emitted from or reflected by a specimen, or has penetrated through the specimen, under a plurality of types of background light respectively having a plurality of different periods with which intensities of the plurality of types of background light vary cyclically. The apparatus contains a first measurement unit which performs a first operation of measuring the first light while illuminating the specimen with second light, to obtain a first measurement result; a second measurement unit which performs a second operation of measuring the first light while illumination of the specimen is stopped, to obtain a second measurement result; a control unit which controls timing of the operations of the first and second measurement units so that the first operation is performed for a first duration beginning at a first time, and the second operation is performed for a second duration having the same length as the first duration and beginning at a second time which is different from the first time by an integer multiple of the least common multiple of the plurality of different periods; and a calculation unit which obtains a third measurement result, which is not affected by the plurality of types of background light, by subtracting the second measurement result from the first measurement result.
Preferably, the optical measurement method according to the seventh aspect of the present invention, or in the optical measurement apparatus according to the eighth aspect of the present invention may have the following additional features (i) to (iv).
(i) Each of the first and second operations may be performed a plurality of times.
(ii) Each of the first and second operations may be performed in synchronization with one of the plurality of different periods of a selected one of the plurality of types of background light.
(iii) In addition to the features of (i) and (ii), each of the first and second operations may be performed in the vicinity of a certain phase of the one of the plurality of different periods, where the intensity of the selected one of the plurality of types of background light is minimized in the certain phase.
(iv) In addition to the features of (i) and (ii), the one of the plurality of different periods may be the minimum period among the plurality of different periods.
According to the seventh and eighth aspects of the present invention, the difference between the beginning times of the first and second operations of measuring the first light is an integer multiple of the least common multiple of the plurality of different periods of the cyclic variations of the intensities of the plurality of types of background light, and the first and second operations are performed for the same length of time. Since the specimen is not illuminated by the second light during the second operation, it is considered that the amount of influence of the plurality of types of background light included in the first measurement result of the first operation will be the same as the amount of the second measurement result of the second operation. Therefore, it is expected that the influence of the plurality of types of background light included in the first measurement result of the first operation will be removed by subtracting the amount of the second measurement result of the second operation from the amount of the first result of the first operation. Thus, a final (third) measurement result can be obtained with high accuracy even when the wavelength ranges of the plurality of types of background light overlap the wavelength range of the light to be measured, which has been emitted from a specimen in response to illumination of the specimen, or has been reflected by or has penetrated through a specimen when the specimen is illuminated.
In order to accomplish the above-mentioned second object, according to the ninth aspect of the present invention, there is provided an optical measurement method for performing measurement of first light, which has been emitted from or reflected by a specimen, or has penetrated through the specimen, under a plurality of types of background light respectively having a plurality of different periods with which intensities of the plurality of types of background light vary cyclically. The method contains steps of: (a) performing a first operation of measuring the first light for a first duration beginning at a first time and having a length equal to an integer multiple of the least common multiple of at least one period among the plurality of different periods, while illuminating the specimen with second light, to obtain a first measurement result; (b) performing a second operation of measuring the first light for a second duration having the same length as the first duration and beginning at a second time which is different from the first time by an integer multiple of the least common multiple of the plurality of different periods other than the at least one period, while illumination of the specimen is stopped, to obtain a second measurement result; and (c) subtracting the second measurement result from the first measurement result, to obtain a third measurement result which is not affected by the plurality of types of background light.
In order to accomplish the above-mentioned second object, according to the tenth aspect of the present invention, there is provided an optical measurement apparatus for performing measurement of first light, which has been emitted from or reflected by a specimen, or has penetrated through the specimen, under a plurality of types of background light respectively having a plurality of different periods with which intensities of the plurality of types of background light vary cyclically. The apparatus contains a first measurement unit which performs a first operation of measuring the first light while illuminating the specimen with second light, to obtain a first measurement result; a second measurement unit which performs a second operation of measuring the first light while illumination of the specimen is stopped, to obtain a second measurement result; a control unit which controls timing of the operations of the first and second measurement units so that the first operation is performed for a first duration beginning at a first time and having a length equal to an integer multiple of the least common multiple of at least one period among the plurality of different periods, and the second operation is performed for a second duration having the same length as the first duration and beginning at a second time which is different from the first time by an integer multiple of the least common multiple of the plurality of different periods other than the at least one period; and a calculation unit which obtains a third measurement result, which is not affected by the plurality of types of background light, by subtracting the second measurement result from the first measurement result.
When the number of the at least one period is one in the optical measurement method according to the ninth aspect of the present invention, and in the optical measurement apparatus according to the tenth aspect of the present invention, the least common multiple of the at least one period is the one period per se.
Preferably, the optical measurement method according to the ninth aspect of the present invention, or in the optical measurement apparatus according to the tenth aspect of the present invention may have the following additional features (v) to (viii).
(v) Each of the first and second operations may be performed a plurality of times.
(vi) Each of the first and second operations may be performed in synchronization with a selected one of the plurality of different periods other than the at least one period.
(vii) In addition to the features of (v) and (vi), each of the first and second operations may be performed in the vicinity of a certain phase of the selected one of the plurality of different periods other than the at least one period, where the intensity of the selected one of the plurality of types of background light is minimized in the certain phase.
(viii) In addition to the features of (v) and (vi), the selected one of the plurality of different periods other than the at least one period may be the minimum period among the plurality of different periods other than the at least one period.
According to the ninth and tenth aspects of the present invention, the first and second operations are performed for the same length of time, and the length is equal to an integer multiple of the least common multiple of at least one period, among the plurality of different periods, of at least one cyclic variation of the intensity or intensities of at least one type of background light corresponding to the at least one period. It is expected that an amount of influence of the at least one type of background light on a measuring operation for an identical length of time will not change regardless of the beginning time of the measuring operation, when the length of time is equal to an integer multiple of the least common multiple of the at least one period of the at least one cyclic variation of the intensity or intensities of the at least one type of background light corresponding to the at least one period. Since the specimen is not illuminated with the second light during the second operation, regardless of the beginning times of the first and second operations, it is expected that an amount of influence by the at least one type of background light included in the first measurement result of the first operation will be the same as the amount of the second measurement result of the second operation. Therefore, it is expected that the amount of influence by the at least one type of background light included in the first measurement result of the first operation will be removed by subtracting the amount of the second measurement result of the second operation from the amount of the first measurement result of the first operation.
In addition, the difference between the beginning times of the first and second operations of measuring the first light is an integer multiple of the least common multiple of the rest of the plurality of different periods other than the at least one period, and the first and second operations are performed for the same length of time. Since the specimen is not illuminated by the second light during the second operation, it is considered that an amount of influence of the rest of the plurality of types of background light other than the above-mentioned at least one type of background light corresponding to the rest of the plurality of different periods other than the at least one period, included in the first measurement result of the first operation, will be the same as the amount of a component of the second measurement result generated by the rest of the plurality of types of background light other than the at least one type of background light. Therefore, it is expected that the amount of influence of the rest of the plurality of types of background light other than the at least one type of background light, included in the first measurement result of the first operation, will be removed by subtracting the amount of the second measurement result of the second operation from the amount of the first result of the first operation.
Thus, it is expected that the amount of influence of all of the plurality of types of background light included in the first measurement result of the first operation will be removed by subtracting the amount of the second measurement result of the second operation from the amount of the first result of the first operation, and a final (third) measurement result can be obtained with high accuracy even when the wavelength range of the background light overlaps the wavelength range of the light to be measured, which has been emitted from a specimen in response to illumination of the specimen, or has been reflected by or has penetrated through a specimen when the specimen is illuminated.
Further, in the fifth to tenth aspects of the present invention, the plurality of types of background light means a plurality of types of background light which are required to be eliminated from the measurement result.